With the recent rapid progress of potable electronic equipment and communication equipment, secondary batteries having a high energy density are strongly desired from the standpoints of economy and size and weight reduction. Prior art known attempts for increasing the capacity of such secondary batteries include the use as the negative electrode material of oxides of V, Si, B, Zr, Sn or the like or compound oxides thereof (JP-A 5-174818, JP-A 6-60867 corresponding to U.S. Pat. No. 5,478,671), melt quenched metal oxides (JP-A 10-294112), silicon oxide (Japanese Patent No. 2,997,741 corresponding to U.S. Pat. No. 5,395,711), and Si2N2O or Ge2N2O (JP-A 11-102705 corresponding to U.S. Pat. No. 6,066,414).
These prior art methods are successful in increasing the charge/discharge capacity and the energy density of secondary batteries, but fall short of the market demand partially because of unsatisfactory cycle performance. There is a demand for further improvement in energy density.
Japanese Patent No. 2,997,741 describes lithium-containing silicon oxide as the negative electrode material in a lithium ion secondary cell. As long as the present inventors have empirically confirmed, the performance of this cell is yet unsatisfactory due to an increased irreversible capacity on the first charge/discharge cycle. It is not definitely described how to prepare the lithium-containing silicon oxide.